text: ### WARNING ### This is an example of what not to do
  
  map_il = {} # fake, empty data (to quiet down the linter)
  
  # # remove non-cook county entries from the features list in map_il
  features = map_il['features']
  features_length_before = len(features)
  for i, feature in enumerate(features):
      if feature['properties']['COUNTYFP10'] != "031":
          del features[i]
  print('removed non-cook county entries from map_il')
  features_length_after = len(features)
  assert features_length_after < features_length_before, "features list should be shorter after removing non-cook-county entries"
  
  """
  Here's the problem with this code: I have a for loop through features,
  but as I delete items from features, the for loop get jacked up
  somehow and behaves unexpectedly.
  The result is that some features with county not
  equal to "031: creep into the resultant map
  """